Water-bearing explosives thickened with a partially hydrolyzed acrylamide polymer

ABSTRACT

Water-bearing explosives thickened with polyacrylamide containing at least 10 percent by weight of carboxylate (-COO-) moieties and having a molecular weight of about from 3 to 15 million.

United States Patent 72] inventor [2]] Appl. No.

[22] Filed [45] Patented [73] Assignee William M. Lyerly Hagerstown, Md.

Nov. 15, 1967 Nov. 23, 1971 E. I. du Pont de Nemours and CompanyWilmington, Del.

Original application Aug. 18, 1966, Ser.

No. 573,206, Pat. No. 3,355,336. Divided and this application Nov. 15,1967,

Ser. No. 683,127

The portion oi the term of the patent subsequent to Nov. 28, 1984, hasbeen disclalmed.

[54] WATER-BEARING EXPLOSIVES THICKENED WITH A PARTIALLY HYDROLYZEDACRYLAMIDE POLYMER 1 Claim, No Drawings Primary Examiner-Carl D.Quarforth Assistant Examiner-Stephen J. Lechert, Jr. Attorney.lohn F.Schmutz ABSTRACT: Water-bearing explosives thickened with polyacrylamidecontaining at least 10 percent by weight of carboxylate (-COO-) moietiesand having a molecular weight of about from 3 to 15 million.

WATER-BEARING EXPLOSIVES THICKENED WITH A PARTIALLY HYDROLYZEDACRYLAMIDE POLYMER CROSS REFERENCE TO PRIOR APPLICATION This is adivisional application of applicant's copending application Ser. No.573,206, filed Aug. 18, 1966, Pat. No. 3,355,336.

This invention relates to improvements in water-bearing explosivecompositions and more particularly, to improvements in water-bearingexplosive compositions thickened with galactomannan.

Considerable commercial interest has developed in the use ofwater-bearing explosives in recent years. Generally, waterbearingexplosive compositions comprise an aqueous solution or slurry ofinorganic oxidizing salts mixed with organic or metallic fuels andsensitizing agents which can also act as fuels. ,7 n 7.

While these water-bearing explosive compositions have many inherentadvantages such as a wide range of explosive properties, and bettersafety characteristics and economy, both in manufacture and use, thereare likewise many difficulties encountered in their use. Among the majorproblems encountered in the use of water-bearing-explosive compositionsare dilution of the explosive composition by water which may be presentin the borehole and the leaching out of the dissolved and undissolved,but water-soluble, oxidizing salts thus leading to changes incomposition which result in losses in explosive power or even infailures to detonate. In addition, even in dry boreholes segregation ofcomponents can take place under certain conditions so that solidcomponents separate into layers above or below the aqueous saltsolutions to the extent that gross inhomogeneity occurs, again leadingto loss of strength and failure to propagate. Many attempts have beenmade in the art to overcome the aforementioned difiiculties.

Galactomannans, particularly guar gum, have found wide utility asthickening or gelling agents in improving the waterresistance ofwater-bearing explosives. However, if the galactomannans are not highlycross-linked, such products gradually segregate and do not meet thestringent water-resistance requirements of current commercialexplosives. On the other hand, guar compositions sufficientlycross-linked for good water-resistance yield relatively immobile gelledmasses which, in some cases, are disadvantageous and difficult to handleand load into boreholes. For example, stiff, nonpourable gels tend tospread and plug boreholes partially filled with water when they strikethe surface of the water. Also, such compositions are somewhat moreinconvenient to remove from contains than more pourable products and donot spread to fill the available space in the borehole leaving voidswhich could present propagation of detonation. The foregoing problemsbecome progressively greater as the diameter of the borehole is reduced.

Substantially linear, water-soluble or water-dispersible vinyl polymersalso have been proposed to gel or thicken waterbearing explosives.However, unless these polymers are crosslinked, as in US. Pat. No.3,097,120, or are present in high concentration, they give very littlebody to the explosives. Furthermore, such polymers are relativelyexpensive.

This invention provides thickened water-bearing explosives which do notsegregate and are water resistant over a wide range of viscosities.Preferred compositions of this invention have a unique combination ofpourability and fluidity coupled with resistance to water andsegregation which makes them particularly suitable in small diameterholes and in holes par tially filled with water.

Accordingly, this invention provides water-bearing explosivecompositions comprising inorganic oxidizing salt, fuel and water, whichimprovement comprises thickening said compositions with the combinationof polyacrylamide and crosslinked galactomannan, the weight ratio ofsaid polyacrylamide to galactomannan being from about 0,l:l to :1, andpreferably M to 5:1. Thickened as used herein refers to compositions inwhich the viscosity of the aqueous phase has been increased, e.g., to10,000 centipoises or more, as well as to gelled products, includingthose gels which are cross-linked.

The polyacrylamide used is a preformed polymer which has a molecularweight of l to 25, and especially 3 to 15 million. Molecular weight canbe determined from the relation:

wherein V is the intrinsic viscosity of the polymer in dl/grams and m.w.is its molecular weight. Intrinsic viscosity can be determined in theconventional manner from inherent viscosity measured in dilute solutionsin water at 30 C. with an Ostwald Fenske Viscometer. Preferred polymershave a pH as a 1 percent by weight solution in water at 30 C. of aboutfrom 6 to 8, and preferably 6.5 to 7.5. Preferably, the polymer containsat least l0 percent by weight of carboxylate (-COO-) moietiesneutralized with alkali, alkaline earth metal or ammonium bases.

Galactomannans which can be used in this invention include, e.g., guargum and locust bean gum, and also other galactomannan gurns whichinclude those from endosperm seeds of leguminous plants such as thesennas, brazilwood, tara, honey locust, paloverde, rattlebox, alfalfagum, clover gum and fenugreek gum. Of these, guar gum is particularlypreferred because of its ready availability, stability and generalcompatibility with aqueous solutions of inorganic oxidizing agents.

The galactomannans are cross-linked in the aqueous solution of theinorganic oxidizing salt to form stable gelled products at relativelylow concentrations of preformed polyacrylamide and galactomannan and toimpart greater strength, cohesiveness and water-resistance to theresulting compositions. Any of the known cross-linking agentsconventionally employed for galactomannans can be used includingpotassium and sodium dichromate; sodium tetraborate as described in US.Pat. No. 3,072,509; soluble antimony and bismuth compounds at a pH offrom about 6 to 13 as in US. Pat. No. 3,202,55 l; and transition metalcompounds as in Ser. No. 343,]40, filed Feb. 6, 1964, the teachings ofeach of which is included herein by reference. Systems, especially thosecomprising soluble antimony and bismuth compounds plus oxidizing agentsare preferred for forming water-resistant, pourable compositions. Theterms "soluble antimony and bismuth compounts" as used herein refer toantimony or bismuth in ionic form, preferably as Sb, Bi, SbO" or BiO ora combination thereof, in the gelation system, for example, in aqueousor aqueous nitrate containing solutions of galactomannan gum during thegelatin reaction. In general, the foregoing is fulfilled by antimony orbismuth compounds soluble to the extent of at least about 1 part permillion in the gelatin system. Examples of antimony or bismuth compoundswhich can be used in the process of this invention include ox ides andorganic and inorganic salts of bismuth and antimony such as antimonyoxide, antimony chloride and antimony oxychloride, antimony sulfate,antimonyl sulfate, antimony tartrate, potassium antimonyl tartrate,sodium pyroantimonate, antimony fluoride, antimony citrate, bismuthoxide, bismuth chloride, bismuth citrate, sodium bismuthate, bismuthnitrate and mixtures thereof. Alkali metal antimony salts of hydroxylatepolybasic acids, particularly potassium antimony tartrate, arepreferred. Oxidizing agents used in combination with the above includehydrogen peroxide, alkali and alkaline earth peroxides, and alkali,alkaline earth and ammonium permanganates, chromates and dichromates.However, alkali metal dichromates, e.g., sodium and potassiumdichromates are especially preferred.

In the process of this invention the particularly preferredcross-linking agent is potassium antimony tartrate and the par ticularlypreferred oxidizing agent is alkali metal, especially sodium orpotassium dichromate. The concentration of antimony or bismuthcross-linking agent based on the amount of galactomannan is about from Ito l5 percent, preferably 2 to 10 percent by weight of potassiumantimony tartrate or an equivalent and about from 0.2 to 5 percent,preferably 0.5 to 3 percent by weight of potassium dichromate.

The rate of gelation and final viscosity of the gelled compositions ofthis invention is related to the kind and concentration of thegalactomannan, the molecular weight and concentration of the preformedpolyacrylamide, and the kind and concentration of the cross-linkingagent. Thus, it will be apparent that the variables are interrelated andconveniently are adjustable to provide a gel having the desiredproperties during manufacture, storage, shipping and use. As indicatedearlier, a particularly preferred composition of this invention is apourable, water-resistant, water-bearing explosive compositioncontaining a ratio of polyacrylamide to guar gum of about from 1/] to/1, most preferably 2/] to 3/1, the total amount of guar gum andpolyacrylamide employed being less than about 2 percent, and preferablyless than 1 percent, by weight of the total explosive composition. Thecross-linking agent, used in the quantities set forth above, will reactwith the guar gum to fonn a gel in the aqueous phase of the blastingcomposition, the polyacrylamide functioning primarily as a thickeningagent. Thicker, i.e., more viscous, less pourable compositions can beobtained by employing a larger weight percentage of galactomannan (guar)and/or polyacrylamide, by employing a higher ratio of cross-linkingagent to galactomannan, by using polyacrylamide of higher molecularweight, and/or by providing a cross-linking system which will provide amore highly cross-linked, stable structure with the galactomannan.

In its broad aspects the improvement of this invention can be applied toany of the known general types of water-bearing explosives fluid at roomtemperature having a continuous phase comprising water. The compositionsof this invention usually contain at least about 20 percent by weight ofan inorganic oxidizing salt. Such salts include ammonium, alkali metaland alkaline earth metal nitrates and perchlorates as well as mixturesof two or more of such salts. Examples of such salts are ammoniumnitrate, ammonium perchlorate, sodium nitrate, sodium perchlorate,potassium nitrate, potassium perchlorate, magnesium nitrate, magnesiumperchlorate and calcium nitrate. Preferably, the inorganic oxidizingsalt component contains at least 45 percent of at least one salt whichis highly soluble in water at room temperature, that is, at least assoluble as ammonium nitrate, and preferably, the aqueous phase in thecomposition contains a substantial portion of ozidizing salt, forexample, 40 to 70 percent by weight thereof. inorganic oxidizing saltmixtures containing at least about 50 percent by weight of ammoniumnitrate and at least about 50 percent by weight of sodium nitrate areparticularly preferred.

The fuels employed in the compositions of this invention can be, forexample, self explosive fuels, nonexplosive carbonaceous and metallicfuels, or mixtures of the aforementioned types of fuels The fuel orfuels used in the compositions of this invention can be varied widely,provided that in the composition in which any particular fuel is used,the fuel is stable, that is, prior to detonation, during preparation andstorage, the fuel is chemically inert with the system. Self-explosive"fuel as used herein refers to a substance which by itself is generallyrecognized in the art as an explosive. Examples of selfexplosive fuelsinclude organic nitrates, nitro compounds, and nitramines such as TNT,pentaerythritol tetranitrate (PETN), cyclotrimethylenetrinitramine(RDX), cyclotetramethylenetetranitramine (HMX), tetryl, nitrostarch,explosive-grade nitrocellulose and smokeless powder, as well as mixturesof the aforementioned self-explosive fuels such as, for example,pentolite (PETN/l NT), Composition B (RDX/T NT) and tetratol (tetryl/TNT). The self-explosive fuel can be, for example, in any of theconventional flake, pelleted or crystalline forms. The amount of fuelvaries with the particular fuel employed. in general, up to 40 and,preferably, to 40 percent by weight based on the weight of compositionof self-explosive fuel is used.

Examples of carbonaceous nonexplosive fuels include finely divided coaland other forms of finely divided carbon; solid carbonaceous vegetableproduct such as cornstarch, woodpulp, sugar, ivory nut meal and bagasse;organic liquids such as hydrocarbon oils, fatty oils and vegetable oils;urea; and mixtures of two or more of the aforementioned carbonaceousfuels are employed.

Metallic fuels include, for example, alumina and iron, and alloys ofsuch metals such as aluminum-magnesium alloys, ferrosilicon,ferrophosphorous, as well as mixtures of the aforementioned metals andalloys. Although, as disclosed in U.S. Pat. No. 2,836,484, up to about50 percent by weight of metallic fuel can be employed in water-bearingcompositions, usually on the order of l to 20, and preferably 1 to 8percent by weight of metals such as aluminum, and on the order of about10 to 30 percent by weight of heavier metallic fuels such asferrophosphorus and ferrosilicon are employed.

Preferably, the total amount of fuel is adjusted so that the totalcomposition has an oxygen balance of from about 30 to +l0 percent and,excepting for those compositions containing 'the aforementioned heaviermetallic fuels such as ferrophosphorus and ferrosilicon, preferably theoxygen balance is between about l 5 to 0 percent.

To further enhance fluidity of the compositions of this in vention,particularly at low temperatures, they can contain 0.25 to 10 percent,and preferably l to 5 percent, based on the total weight of compositionof fluidizing agent as described in U.S. Pat, No. 3,190,777, which isincorporated herein by reference. Preferred fluidizing agents includedimethyl sulfoxide, methanol, fonnamide and methyl cellosolve.

As previously indicated, the composition of this invention contain atleast about 5 percent by weight of water. The waterbearing compositionsto which this invention is directed generally contain less than about 45percent by weight of water and, preferably on the order of about 10 to30 percent by weight of water based on the total composition.

In general, the explosive compositions of this invention can be preparedby the conventional formulating techniques used for preparinggalactomannan or cross-linked galactomannan aqueous explosives.Preferably, however, the galactomannan, mixed with soda, preformedpolyacrylamide and fuels is added to a hot (l00200 F.) concentratedsolution containing the major proportion of oxidizing salt, then thecross-linking agents are added, the solution is mixed and the productpacked. It has been found particularly advantageous for improved uniformdispersion to add approximately one-third of the ammonium nitrate liquorfirst, then to add the remaining ingredients, and finally, after about30 seconds, add the balance of the ammonium nitrate liquor.

This invention provides a means for making water-bearing explosivecompositions having excellent water-resistance in products varying incharacteristics from pourable fluids to moldable, tough plastic masses.The compositions of this invention have excellent cohesiveness over awide range of viscosities. Furthermore, the improvement of thisinvention alters the crystal growth of inorganic salts, reduces crystalsize, and improves sensitivity. When measured at 25 C. in the aqueousphase without solids, the preferred fluid compositions have a viscosityof about from 100,000 to about 400,000 centipoises, preferably l50,000to 300,000 centipoises, as measured on a Brookfield Synchrolectricviscometer, Model RVT with a helipath attachment using a TC spindle at 1rpm. These fluid compositions are particularly outstanding in their easeof packing and loading and the facility with which they fill boreholesyet resist segregation, leaching and dilution in the presence of water.Such fluid products are also eminently suited for rapid loading in smalldiameter holes giving ease in borehole loading which has heretofore onlybeen obtainable with products blended in situ at the blasting site,e.g., in slurry trucks, but economically infeasible for use in smallerblasting operations.

As previously indicated, the explosive compositions of this inventioncan vary from pourable fluids to moldable, tough plastic masses, allhaving excellent water-resistance and excellent cohesiveness.Particularly preferred compositions of this invention are pourableexplosive compositions having a viscosity of 150,000 to 300,000centipoises, and containing,

by weight, 20 to 60 percent ammonium nitrate alone or in combinationwith [0 to 40 percent sodium nitrate; 15 to 40 percent fuel, preferablyTNT; to 30 percent water; 0.1 to 0.5 percent guar gum; 0.2 to L0 percentpreformed polyacrylamide; and, based on the weight of galactomannan,about from 0.5 to 3 percent of oxidizing agent, preferably an alkalimetal dichromate such as sodium or potassium dichromate and 2 to 10percent of an antimony compound soluble in the system, preferablypotassium antimony tartrate.

The compositions of this invention possess greater fluidity,homogeneity, resistance to disintegration or leaching by water andstability, i.e., resistance to degradation and settling out ofcomponents, than compositions which contain only substantially linear,water-soluble or water-dispersible vinyl polymers or those which containonly cross-linked galactomannans. This greater fluidity, homogeneity,stability and water-resistance is particularly advantageous when thecompositions are to be used in wet locations, since disintegration andleaching of a composition by water, if such occurs, can lead to failuresto detonate or to propagate a detonation throughout the length of anexplosive column. if the explosive structure degrades, i.e., by virtueof disintegration of the gel structure, subsequent segregation ofcomponents, particularly undissolved (solid) fuels and sensitizers, canoccur under the force of gravity, and the components in a borehole,whether in a container or cartridge, shucked therefrom, or simply pouredinto a borehole will become so heterogeneous that complete failure ofdetonation or propagation of detonation through the entire length of thecolumn of the explosive charge will occur. Further, the compositions canbe packaged in contains compatible with the ammonium nitrate liquoremployed, e.g., of polymeric materials, and stored until time of usewithout deterioration or separation of components. Even when freed fromthe container these compositions retain an optimum degree of resistanceto disintegration and leaching by water which may be already present inthe borehole or which may enter the borehole after the compositions areloaded. With the compositions of this invention, bottom of the holeloading is not required. Likewise, the material will not block aborehole as a conventional water gel very often does. The higher loadingper foot of borehole and speed of loading compared to either cartridgedproducts or normal water gels are significant advantages which aremanifest in the compositions of this in vention.

in the following examples which illustrate this invention parts,percentages and ratios are by weight unless otherwise indicated.

EXAMPLES 1 TO 5 Water-bearing explosive compositions of this inventionare prepared from the materials noted in table I. The formulations areprepared in a rotary mixer in the following sequence of steps:

1. One-third of 65 percent ammonium nitrate solution at l50l70 F., isplaced in the mixer, and to the ammonium nitrate solution, withcontinuous agitation, is added 6 to 8 mesh pelleted TNT or smokelesspowder, hydrocarbon oil Corvus" oil), metal fuels and/or sulfur asindicated in the Table. 1

2. A premixed composition of sodium nitrate, polyacrylamide andgalactomannan is added and the contents of the resulting mixture areagitated for seconds.

3. The balance of the ammonium nitrate liquor and formamide, where used,are added and the contents of the mixture are agitated for 3-% minutes.

4. The oxidizing agent is added and incorporated in the blend byagitating for 15 seconds.

5. Cross-linking agent is added and the blend is mixed 30 seconds more.

6. Cfontents of mixer are discharged into polyethylene bags.

TABLE I Example 1 2 3 4 5 65% AN liquor 50 57 50 42 30 (Ammoniumnitrate). (32. 5) (37) (32. 5) (27. 3) (20) (Water) (17. 5) (20) (17. 5)(14. 7) (10) Sodium nitrate. 20. I) 18.0 20. 0 21.0 20.0 TNT Smokelesspowder Al num Ferrophosphorus S ur The compositions also contain perhundred weight:

Corvus oil, lbs 0. 25 0. 25 0. 25 Formamide... 2.0 2.0 2.0 Guar gum, lbs0. 3 0. 2 0. 2 0. 2 Polyacrylamlde, lbs 0. 8 0. 5 0. 4 1.0 5% solution,Kzcl'zo7, cc... 25 25 10 10 30 5% PAT, cc 100 100 45 V '45 V 60Velocity, m./sec., 70 F 3 4, 104 4 3,900 3 4, 104 5 4,200 3 4, 800Density, g./cc 1. 4 1. 5 1. 4 1. 1. 45

Molecular wt.: 5-5 million; pH of 1% solution in H O-7; neutralizedcarboxylate 10%.

1 Potassium antimony tartrate.

3 Tested in S-inch diameters in air.

4 Tested in 4- nch diameters in air.

5 Tested in 5-inch diameters in air.

In examples 1 to 4, the finished compositions are pourable,water-resistant gels having a density of from about L45 to about 1.65g/cc. and a pH of about 7 to 9. The viscosity of the compositions isfrom about 100,000 to 400,000 cps. The composition in example 5 is astiff water-gel suitable for use in mudcapping operations. All thecompositions in table I are uniform in appearance and composition, andundissolved components remain uniformly dispersed. Even when thecompositions are dropped approximately 40 or more feet into water, noevidence of breakdown of the gel structure is noted. No evidence ofincompatability with water-filled boreholes is found, Deliberateattempts to plug a borehole with compositions of examples l to 4 are notsuccessful. The formulations in examples 1 to 4 will flow through al-inch-diameter funnel at F., and have sufficient water-resistancewhereby bottom of the hole loading is not required. The compositions arenot capsensitive but can be detonated by a conventional 25 g RDX primerand detonate with a velocity of about 4100 meters/second in aZ-inch-diameter column.

in the foregoing examples, similar results are obtained when a bismuthcompound or a transition metal compound, especially TYZOR LA, isemployed in place of the potassium antimony tartrate as thecross-linking agent for the galactomannan.

"Titanium-antimonium lactate E. I.

available from E. l. du Pont de Nemours & Company EXAMPLES 6-10 In orderto evaluate the stability of the gelled water-bearing explosivecompositions of this invention and to compare them with compositionscontaining only polyacrylamide or only guar gum, a sample of eachcomposition, described in table ii, and prepared by the generalprocedure of examples 1 to 5 is placed in a tightly closed glasscontainer in a chamber maintained at 20 F. The composition in example 7which contains only guar gum becomes hard at this temperature, is notpourable, and separation of the ingredients occurs in a matter of hours.All the other compositions are pourable, water-resistant compositions atthis temperature. About four weeks later, the compositions in examples6, 8, 9, and I0, which are still pourable, coherent, water-resistantgels, are transferred to a chamber maintained at F. This isrepresentative of a moderately high temperature which might beexperienced in a field storage magazine or a service truck. Thecompositions stored at 100 F. are inspected at intervals for evidence ofdeterioration such as obvious softening and clumping of gel ganicoxidizing salt, fuel and water, the improvement which million determinedfrom the relation V=3.73 l (m.w.)-, wherein V is intrinsic viscosity inposition, per hundred weight liquor TNT nitrate I claim: 1. ln thickenedwater-bearing explosives comprising inor- TABLE II Composition, percentby wt. Com X llgxample 65% AN Sodium Formamige, Gumgum,

Polyacryl- "Corvus" PAT, 0 Time or bs. amide, lbs. oil, lbs. cc.

cc. deterioration base salts.

l t i I t

